The workbench · Version 1.0
Email CSV migration checker
Find structural and mapping problems before opening an importer. Your CSV stays in this browser. The result is a review list, never permission to send or approval to import.
Checks quoted CSV structure, recognizable email headers, uneven records, potential duplicate addresses, blank values in the first recognized Name or First Name column, and selected source-status labels. It does not inspect every mapped field. Review all blank fields before import, including last names and custom fields. It compares two documented import contracts: Kit and MailerLite. Neither vendor requires our exact sample headers; you still map fields in its importer.
Check a local file
Try synthetic files first
Kit mapping example has four records, one potential duplicate, one blank email and one blank first name. Its source-status labels are illustrative, not Kit’s required input fields. MailerLite mapping example has three records, one positive source-status label, one do-not-send label and one unknown. All addresses use example.com and are invented.
Two documented contracts, not a compatibility seal
| Concern | Kit | MailerLite |
|---|---|---|
| Minimum mapping | Header row and at least an email-address column; map columns to fields. | Match spreadsheet columns to subscriber fields; the help example uses Email, Name, Company and Country. |
| Empty values | Imported blank field values can replace existing data. Split imports to preserve values. | An import setting controls updating subscriber fields with empty data. |
| Organization | Comma-separated tags are mapped explicitly; additions can activate automations. | Tags/Groups can create groups; an import setting controls group-triggered automations. |
| What this checker cannot see | Your account’s current subscribers, suppression state, field settings, trigger rules, actual address validity or evidence of permission. | |
Method and limits
The parser supports quoted separators, doubled quotes, quoted newlines, CRLF/LF and a UTF-8 byte-order mark. It rejects unclosed quotes and characters after a closing quote. Spaces outside a quoted field are not silently repaired. Email checks are only a basic shape heuristic, not mailbox verification. Potential duplicates are compared after trimming and lowercasing; nothing is merged or deleted. Repeated addresses with different status classes are counted separately as conflicts or uncertainty. Multiple recognized status columns produce unknown counts instead of silently choosing the first. Blank physical lines are skipped, but records containing delimiters or quoted empty fields are counted.
Recognized source labels include yes/active/subscribed and no/unsubscribed/bounced/unconfirmed. Unknown values remain unknown. A positive label is not proof of consent. Tags, purchases and an address are never promoted to permission. Formula-like cells are counted as plain text; no cell is evaluated or rewritten. Report downloads contain counts and generic warnings, not names, addresses or the original headers.
Privacy and a useful next step
The tool does not upload, save to local storage, log or send your file. It reads the selected bytes in browser memory. Clear resets the selected file and displayed report. It is not a secure memory eraser; the browser controls memory reclamation. Your browser or device may have its own file history. No analytics event records file contents. Keep an unchanged source copy and reconcile statuses separately in the Mailchimp-to-MailerLite guide or Kit’s field-mapping workflow.
Official sources
- Kit: import a subscriber list (read November 7, 2026).
- MailerLite: import subscribers (read November 7, 2026).
Part of Email marketing. The calculation is useful without buying or signing up.
Citation and revision
The Guide Index, “Email CSV migration checker”, version 1.0, November 7, 2026. Canonical: https://theguideindex.com/tools/email-migration-checker/. Original calculations and synthetic examples, not a vendor test or certification.